. Put it another way and consider that Canon 70d has half the sensor for PDAF. Is the IQ terrible?

doesn't the Canon like all DSLR's have a separate PDAF sensor?

there is a huge difference between a camera with on sensor PDAF where pixels on the sensor are removed and replaced with focus sensors than a DSLR that has all of the focus sensors in a completely different sensor that is not a part of the image forming sensor

seriously - you do realize that DSLR's have a completely separate focus detect array that is in the bottom of the camera below the mirror - dont you?